Duplex bars(also known as back-to-back bars) are assembled using the same spacer colour as the perimeter (either in aluminium or warm-edge), and held together through use of the key system. When an external bead is applied to the outer face of the glass over the duplex bar, it creates the look of small individual units. It is possible to assemble curved grids or special designs if a template is provided. Bars are available in the following colours: